In one practiced method of the kind mentioned above, the lathe operator engaged with the reprofiling of the wheels of not disassembled wheel sets lets the wheel set run into the machine and probes with his turning tool for that point on the tread surface which, according to his visual impression, shows the greatest wear. He therefore runs the tool to that wear location which, according to his subjective impression, is most pronounced. In this connection the operator must confine himself in his judgement and adjustment to the tread surface of the wheel and cannot use the flange for this purpose, which however, has special significance as far as the wear is concerned and is therefore decisive for the final new profile.
If considerable flange wear is present, the flange determines the cutting depth required for reprofiling. However, the operator cannot determine this, rather, he takes the tread surface for his orientation. The operator must rely, after several test cuts, on finally producing a completely cut-over profile having an entirely machined, shiny surface. To get to this completely cut-over profile as quickly as possible, there is the temptation for the operator, because he is on piece work, to take cuts as deep as possible, even if this is actually not necessary. In this manner, valuable wheel tire material is cut off needlessly.
Following this, because in the lathe, the diameter differences of the two wheels in the respective measuring circle plane cannot be ascertained, the wheel set must be rolled out of the turning machine and rolled into a measuring machine, by means of which the diameter difference is determined. Subsequently, the wheel set is placed in the turning machine again to make a corrective cut for producing equal diameters at both wheels. In practice, turning machines also have become known which are already equipped with friction-wheel measuring devices for determining the diameters of the wheels of a wheel set. In this way, the rolling-in and out which is necessary for the measurement, after a shiny profile is produced, may be omitted.
In wheel set turning machines working with centers it is also known to determine prior to the reprofiling, by means of a frictionwheel measuring device rolling on the tread surface of each wheel of a wheel set being rolled into turning machines, the actual diameter of the two worn wheels in the measuring circle plane of each wheel. The turning tool is then adjusted to the smallest diameter of the two wheels of a wheel set and the wheels of a set are then reprofiled with this tool adjustment. However, this known method also does not take into account the flange wear, so that one must carefully probe the wear condition of the flange by repeated cuts. This is time-consuming and therefore leads the lathe operator who is on piece work, to adjust the turning tool by his "feel" to so deep a cut that he obtains with a single cut a completely renovated profile and needs to correct only the diameter difference in the second cut. Therefore, this known method is not a solution, either.
It is also known to underpin and thus to fix the bearing boxes of the wheel sets in the turning machine for reprofiling of not disassembled railroad wheel sets. With this arrangement, it is made sure that the axis of rotation of the wheel set to be machined retains a constant position during the machining, as is also the case when turning between centers. It is a disadvantage in this known method that no reference surfaces with the necessary accurate machining and correspondingly accurate dimensional tolerances are provided at the bearing boxes, since the bearing boxes are, as a rule, castings with relatively rough tolerances. While the axis of rotation is thus fixed in its position during the turning operation, due to the support in the bearings, its position is unknown, so that reference to the axis of rotation for the diameter adjustment of the tools is not possible.
In turning between centers, the need to ascertain the diameter difference in a separate measuring operation is eliminated, as the position of the axis as well as the position of the tools relative to the axis are always known. However, it is often difficult to expose the center marks in the assembled wheel sets, since the bearing boxes of the wheel sets must be partly disassembled for this purpose. These center marks also are often damaged, so that it is no longer possible to clamp the wheel set correctly. In addition, only definite axle loads up to a limited maximum value can reasonably be taken up between centers as there is otherwise, for instance, in the case of heavy locomotives, the danger that the center marks and the points of the turning machine are plastically deformed and thus destroyed.
German Patent No. 1,552,335, which corresponds to U.S. Pat. No. 3,518,914, describes a sensor arrangemnt for the tool positioning prior to the copy turning of run-down, unmeasured wheel tires of track vehicles in which set turning machines having separate feed carriages and a copying device. The copying device has a copying feeler arranged on its cross slide and a template arranged on its feed carriage. In this known apparatus a plurality of sensors which may be moved along with the feed carriage is provided, which are positioned with their feeler or sensor points approximately perpendicularly to the original profile and which scan the profile at the worn places independently of each other. Their stroke movements, which are caused by the feed carriage motion and the worn places of the profile, act individually on end switches which are connected in parallel and stop the drive of the feed carriage as soon as all switches remain closed when the wheel set continues to rotate.
These sensor arrangements are used in such wheel set turning machines which machine the wheel set held between centers. Since both cross slides are advanced in the radial direction simultaneously and by the same amount until the last end switch of the two sensor devices remains closed, and since the reference base is known because of the center mounting, both wheels of a set are reprofiled simultaneously to the same diameter. According to this prior art, these sensor devices can thus be used only if the position of the reference base is known and fixed.